The present invention relates generally to telecommunication systems. More particularly, the present invention relates to impedance blocking filter circuits used in telecommunication systems for interconnecting between incoming telephone lines from a telephone company""s central office and subscriber or customer telephone equipment.
Frequently, subscribers or customers of telephone service also have, in addition to one or more telephone handsets, a personal computer which requires telephone line access to the Internet or other computer networks. As is known in the art, a computer user can in some instances receive DSL (an acronym for Digital Subscriber Line) signals from the Internet over the same telephone lines via an Internet Server Provider (ISP). In order to increase the speed of downloading of information from the Internet, a DSL network interface is typically purchased and installed between the incoming telephone lines and the user""s computer. However, since one or more of the telephone subscriber""s terminal equipment devices (such as telephone sets, facsimile machines and/or answering devices) may also be connected to the same incoming telephone lines via internal house wiring, DSL interference problems may be caused by the terminal equipment. This can significantly limit or reduce the data rate of the DSL signals.
Telecommunication industry standards, such as described in ANSI""s (American National Standard Institute) draft document T1E1.4/2001-007R, generally require the use of impedance blocking circuits between DSL lines from a phone company and a subscriber""s terminal equipment (telephone handsets, fax machines, etc). Impedance blocking filter circuits for such use are known. For example, U.S. Pat. Nos. 6,181,777 and 6,212,259, each to F. Kiko and entitled IMPEDENCE BLOCKING FILTER CIRCUIT, teach circuits which can be used for this purpose. However, some impedance matching circuits designed for this purpose are fairly complex. As a result, some of these circuits are more expensive to produce than is desired. Further, some of these impedance matching circuits are relatively difficult to adjust for use with different telephone systems having different impedance matching and other requirements.
Accordingly, it would be desirable to provide an impedance matching or blocking filter circuit, for connection between a DSL line and a customer""s telephone terminal equipment, which is inexpensive to manufacture and easily adaptable to different telephone systems.
An impedance blocking filter circuit is used in telecommunication systems for interconnecting between incoming telephone lines carrying Digital Subscriber Line (DSL) signals and a customer""s terminal equipment in order to block impedances above a desired frequency. The impedance blocking filter circuit includes a low pass filter circuit having at least one capacitive pole providing component. The impedance blocking filter circuit also includes a tank circuit coupled in series with the at least one capacitive pole providing component to provide impedance matching for the customer""s terminal equipment.